Die cushion device

ABSTRACT

After molding is started, a large reaction force is obtained by compressing the air within a lower chamber by a piston while maintained in a sealing state. At an intermediate time of the molding, a small reaction force is obtained by communicating the upper and lower chambers with each other by a switching portion of a spool. At a final time of the molding, a large reaction force is again obtained by interrupting a flow path between the upper and lower chambers. The die cushion ability can be mechanically switched in association with the stroke of the piston, the die cushion device can be set such that no time lag is easily caused at a switching time, and the die cushion ability can be instantly switched.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a die cushion device, e.g., adie cushion device preferably used in deep drawing molding using apress.

[0002] In a press working field of a sheet metal, etc., a die cushiondevice is conventionally arranged below or within a bed of a pressmachine, and upward reaction force is applied to a lower die by airpressure, etc. so as to preferably perform the press working.

[0003] In the main current of a structure of such a die cushion device,the air within a cylinder set to a predetermined pressure is compressedby lowering a piston, and reaction force caused at that time isutilized.

[0004] In accordance with Japanese Utility Model Publication No.24916/1978 and Japanese Utility Model Laid-Open No. 109817/1987, it isproposed that a plurality of such cylinders are arranged in series, andpistons lowered within the respective cylinders are connected to eachother, and a supply source of the compressed air and an air chamberwithin each cylinder compressed by the piston are communicated with eachother through an electromagnetic valve.

[0005] In the die cushion device described in each of these officialgazettes, for example, smallest die cushion ability can be realized byselectively opening and closing the electromagnetic valve if thecompressed air is supplied to only one air chamber, and largest diecushion ability can be realized if the compressed air is supplied to allthe air chambers. Thus, the die cushionability can be changed byselectively opening and closing the electromagnetic valve Further, thelatter official gazette discloses that the compressed air is alsosupplied by switching the electromagnetic valve to the air chamber on anupper side increased in volume by lowering the piston, and a pressurereceiving face of this piston facing the interior of the air chamber onthe upper side is set to have an area smaller than that of a pressurereceiving face of this piston facing the air chamber on a lower side.

[0006] In such a construction, large die cushion ability can be realizedby supplying the compressed air to only the air chamber on the lowerside, and small die cushion ability according to the difference in areabetween the pressure receiving faces can be realized by supplying theair pressure to both the upper and lower air chambers. Therefore, thedie cushion ability can be changed even when one cylinder and one pistonare used.

[0007] In the case of deep drawing molding of a thin plate material,etc., it has been found that it is a useful processing method forimproving the quality of molding parts to change a holding degree of thethin plate material in a blank holder by changing the die cushionability during one stroke as follows.

[0008] That is, at an initial stage at which an upper die begins topress the thin plate material, reaction force in the die cushion deviceis increased so as to firmly hold the thin plate material. At a moldingstage from the start of the drawing, the reaction force is reduced so asto preferably perform the drawing. At a final stage at which the moldingis terminated, the reaction force is again increased so as to reliablymold an outer shape.

[0009] However, in the conventional die cushion device, the die cushionability is the same as long as the same part is molded if the diecushion ability is once set at a planning time of the press machine.Accordingly, in the conventional die cushion device, a problem exists inthat it is impossible to cope with the above-mentioned processing methodfor changing the die cushion ability during one stroke (during one cycleof the piston of the die cushion device) at a molding time.

[0010] Further, the die cushion ability was changed on trial during onestroke by switching the opening and closing of the electromagnetic valveof the conventional die cushion device during one stroke. However, aproblem exists in that responsiveness of the electromagnetic valve isbad and no die cushion ability can be smoothly changed.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide a die cushiondevice able to smoothly change die cushion ability during one stroke ata molding time.

[0012] In a mode of the invention for achieving this object, a diecushion device comprises first and second chambers arranged within acylinder and divided by a piston slid within the cylinder and ischaracterized in that control means for controlling inflow and outflowof a fluid between the first and second chambers in association with astroke of the piston is provided.

[0013] In accordance with this die cushion device, the inflow andoutflow of the fluid between the first and second chambers arecontrolled by the control means between strokes of the piston, i.e.,during one stroke at a molding time. In this case, when die cushionability is reduced, the flow path between the first and second chambersis communicated by the control means, and the piston is moved whilefluid pressures of the first and second chambers are maintained at anequal pressure. In contrast to this, when the die cushion ability isincreased, the flow path between the first and second chambers isinterrupted so as to reliably generate reaction force required in themolding by a compressing action within the second chamber.

[0014] Since the control means mechanically controls the inflow andoutflow of the fluid between the first and second chambers inassociation with the stroke of the piston, movements of the fluid atcommunicating and interrupting times of the flow path between the firstand second chambers are rapidly switched so that the die cushion abilitycan be smoothly changed.

[0015] In this die cushion device, the control means is desirablyconstructed by including a valve body arranged within the cylinder.

[0016] Since the control means constructed by the valve body is arrangedwithin the cylinder by this construction, compactness of the die cushiondevice is promoted.

[0017] In this die cushion device, the control means is desirablyconstructed by including a switching device arranged outside thecylinder.

[0018] In accordance with this construction, since the control means isconstructed by the switching device arranged outside the cylinder, noswitching device is easily limited in structure, size, etc. so that thedegree of freedom on design is increased.

[0019] In this die cushion device, it is desirable that the piston isslid by a rod, and pressure exhaust means for exhausting a fluidpressure within the first chamber on this rod side is arranged.

[0020] In accordance with this structure, there is a case in which thepiston compresses the fluid within the first chamber at a completingstage (a returning stage of the piston to a stroke end on a rod side) ofone cycle of the piston.

[0021] In such a case, when the compressed fluid exists within the firstchamber, there is a possibility that no piston is perfectly returned toa correct position. Therefore, in the construction of the invention, thefluid pressure due to such a fluid is exhausted by the pressure exhaustmeans so that the piston can be reliably returned to the correctposition.

[0022] Furthermore, a plurality of the control means may be alsoarranged in the die cushion device of the invention.

[0023] In accordance with this construction, the fluid is stepwise movedby the plural control means. If this construction is used in the diecushion device of a multistage type having cylinders and pistonsaccording to the number of control means, it is also possible to providea die cushion device having larger reaction force, i.e., larger diecushion ability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a sectional view showing a die cushion device inaccordance with a first embodiment mode of the present invention.

[0025]FIG. 2(A), FIG. 2(B), and FIG. 2(C) are views for explaining theoperation of a control means constructed by a valve body in the diecushion device of the first embodiment mode.

[0026]FIG. 3 is a time chart showing a generating situation of upwardreaction force against external force applied to the die cushion deviceof the first embodiment mode.

[0027]FIG. 4 is a sectional view showing a die cushion device inaccordance with a second embodiment mode of the invention.

[0028]FIG. 5 is a sectional view showing a die cushion device inaccordance with a third embodiment mode of the invention.

[0029]FIG. 6 is a perspective view showing one constructional part of acontrol means constructed by a rotary valve in the die cushion device ofthe third embodiment mode.

[0030]FIG. 7(A), FIG. 7(B), and FIG. 7(C) are views for explaining anoperation of the control means constructed by the rotary valve in thedie cushion device of the third embodiment mode.

[0031]FIG. 8 is a sectional view showing a die cushion device inaccordance with a fourth embodiment mode of the invention.

[0032]FIG. 9(A), 9(B), and 9(C) are views for explaining the operationof a control means constructed by a valve body in the die cushion deviceof the fourth embodiment mode.

[0033]FIG. 10 is a sectional view showing a modified example of theinvention.

[0034]FIG. 11 is a sectional view showing another modified example ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Each embodiment mode of the present invention will next beexplained on the basis of the drawings.

[0036] A first embodiment mode will first be explained.

[0037]FIG. 1 is a sectional view showing a die cushion device 1 inaccordance with a first embodiment mode of the present invention. FIG.2(A), FIG. 2(B), and FIG. 2(C) are views for explaining the operation ofa control means constructed by a valve body in the die cushion device 1.FIG. 3 is a time chart showing a generating situation of upward reactionforce F against external force P (FIG. 1) applied to the die cushiondevice 1.

[0038] In FIG. 1, the die cushion device 1 is of a pneumatic type havinga cylinder 10 of a cylindrical shape having a bottom, a disk-shapedpiston 20 slid in a vertical direction in FIG. 1 within the cylinder 10,and a spool 30 extending through the cylinder 10 and the piston 20.

[0039] An insertion hole 12 inserting a rod 21 of the piston 20thereinto, and an insertion hole 13 for inserting the spool 30 thereintoare arranged in an upper face portion 11 of the cylinder 10. Aninsertion hole 15 for inserting the spool 30 thereinto is also arrangedin a bottom face portion 14.

[0040] Sealants 16, 17 coming in close contact with the spool 30 andsecuring inside and outside airtight properties of the cylinder 10 arearranged in the insertion holes 13, 15.

[0041] An upper chamber 18 as a first chamber is formed above the piston20 within the cylinder 10, and a lower chamber 19 as a second chamber isformed below the piston 20.

[0042] Similar sealants are also arranged around the insertion hole 12and the piston 20 although these sealants are omitted in FIG. 1. Theinside and outside seal properties of the cylinder 10 and the airtightproperty between the upper chamber 18 and the lower chamber 19 aresecured by these sealants.

[0043] First, an air intake port 141 communicated with the lower chamber19 is arranged on a side of the bottom face portion 14, and a flow path142 is connected to this air intake port 141. Compressed air is flowedinto the lower chamber 19 through this flow path 142 and the air intakeport 141 so that the interior of the lower chamber 19 is filled with thecompressed air.

[0044] In contrast to this, an exhaust port 111 is arranged in the upperface portion 11, and an electromagnetic valve 113 is arranged in theexhaust port 111 through a flow path 112.

[0045] A bypass flow path 143 is arranged between the flow paths 112 and142, and a check valve 144 as an exhaust pressure means is arranged inthe bypass flow path 143. The check valve 144 is opened when the airpressure within the upper chamber 18 is equal to or greater than the airpressure within the lower chamber 19. Thus, the check valve 144 has afunction for maintaining the interior of each of the chambers 18, 19 atan air pressure A.

[0046] A die cushion pad 22 is attached to an upper portion of the rod21 of the piston 20, and downward external force P is applied to thisdie cushion pad 22 by the movement of a slide of an unillustrated pressmachine.

[0047] Further, a communication hole 23 is vertically communicated inthe piston 20, and a spool 30 extends through the interior of thecommunication hole 23. A sealant 24 for performing sealing between thecommunication hole 23 and the spool 30 is arranged in the communicationhole 23.

[0048] A pressure receiving area of an upper face 26 of the piston 20facing the upper chamber 18 is smaller by a sectional area of the rod 21than the pressure receiving area of a lower face 27 of the piston 20facing the lower chamber 19. Therefore, when no external pressure P isapplied and both the pressures within the upper and lower chambers 18,19 are maintained at the air pressure A, force for raising the piston 20becomes larger than force for lowering the piston 20 so that the piston20 is automatically raised.

[0049] A flange 31 is arranged at an upper end of the spool 30, and thespool 30 is detachably fixed to the upper face portion 11 of thecylinder 10 by a bolt 32 inserted into this flange 31.

[0050] A switching portion 33 having a diameter smaller than thediameters of other portions is arranged at a predetermined length in anintermediate portion of the spool 30 in its vertical direction. The flowpath between the upper and lower chambers 18, 19 is communicated whenthe insertion hole 23 of the piston 20 reaches a position of theswitching portion 33. An upper side of the switching portion 33 is setto an upper large diameter portion 34, and a lower side of the switchingportion 33 is set to a lower large diameter portion 35. The flow pathbetween the upper and lower chambers 18, 19 is interrupted when thecommunication hole 23 reaches positions of the upper and lower largediameter portions 34, 35.

[0051] That is, in this embodiment mode, the valve body as the controlmeans in the invention is constructed by the piston 20 having thecommunication hole 23, and the spool 30 having the switching portion 33and the upper and lower large diameter portions 34, 35.

[0052] A diameter, a length and a position of the switching portion 33,the shapes of R-portions on upper and lower end sides of the switchingportion 33, etc. are optionally determined in consideration of dampingtiming of the required reaction force F, a time for damping the reactionforce F, power in damping and generating the reaction force F, etc.

[0053] An operation of the die cushion device 1 and a change in thereaction force F caused by a stroke of the piston 20 will next beexplained with reference to FIGS. 2(A), 2(B), 2(C), and 3.

[0054]FIG. 2 (A): First, compressed air is supplied into the lowerchamber 19 in advance in a state (illustrated by a two-dotted chain linein FIG. 1) in which the piston 20 is located in an uppermost portionwithin the cylinder 10. In this state, a thin plate material begins tobe molded, and downward external force P is applied onto the die cushionpad 22.

[0055] Thus, the piston 20 is lowered and the air within the lowerchamber 19 is compressed so that reaction force F opposed to theexternal force P is caused. The reaction force F is raised as the piston20 is lowered. The upper chamber 18 above the piston 20 becomes a lowpressure (points 0 to S1 in FIG. 3).

[0056]FIG. 2(B): Next, when the piston 20 is continuously lowered, thecommunication hole 23 of the piston 20 reaches the switching portion 33of the spool 30. When the piston 20 then reaches a perfect releasingposition of close contact of the upper large diameter portion 34 of thespool 30 and the sealant 24, the upper and lower chambers 18, 19 arecommunicated with each other, and one portion of the air compressedwithin the lower chamber 19 is instantly moved from the communicationhole 23 to the upper chamber 18 so that both the interiors of the upperand lower chambers 18, 19 are switched to the air pressure A. In thiscase, the reaction force F is also instantly damped (S1 to S2 in FIG.3).

[0057] Thereafter, while the air pressure A within the upper and lowerchambers 18, 19 are slightly raised, the piston 20 is continuouslylowered. The reaction force F in the mean time includes upward force dueto the difference in pressure receiving are a between the upper face 26and the lower face 27 of the piston 20, and also includes forceaccording to a raising amount of the air pressure caused by slightlycompressing the air of the lower chamber 19 by fluid resistance causedwhen the air is moved from the lower chamber 19 to the upper chamber 18.However, this change in the reaction force F is restrained to a smallvalue (S2 to S3 in FIG. 3).

[0058]FIG. 2 (C): When the piston 20 is continuously lowered, thesealant 24 of the communication hole 23 gradually passes through theswitching portion 33 and comes in close contact with an outercircumference of the lower large diameter portion 35 of the spool 30 sothat the flow path between the upper and lower chambers 18, 19 isinterrupted. The lower chamber 19 begins to be compressed from thisstage, and the reaction force F is again raised greatly (S3 to S4 inFIG. 3).

[0059] Subsequently, when the slide of the press machine is lowered to alowermost point and is reversely raised, the pressure within the lowerchamber 19 begins to be returned to the air pressure A from thecompression state. Therefore, the piston 20 is pushed up to a positionprior to the compression so that volume of the lower chamber 19 isincreased and volume of the upper chamber 18 is reduced (S4 to S5 inFIG. 3).

[0060] Then, both the pressures within the upper and lower chambers 18,19 approximately equally approach the air pressure, but the piston 20 isautomatically continuously raised by the above difference in thepressure receiving area. Thereafter, when the sealant 24 reaches theswitching portion 33 of the spool 30, the air is moved from the upperchamber 18 to the lower chamber 19, and the piston 20 is raised whilethe interiors of the upper and lower chambers 18, 19 are maintained atthe air pressure A (S5 to S6 of FIG. 3).

[0061] Thereafter, while the piston 20 is raised, the sealant 24 of thecommunication hole 23 passes through the switching portion 33 of thespool 30. When the sealant 24 comes in close contact with an outercircumference of the upper large diameter portion 34 of the spool 30,the piston 20 begins to compress the interior of the upper chamber 18.However, the check valve 144 is opened simultaneously when the pressurewithin the upper chamber 18 is raised by this compression. Therefore,the upper and lower chambers 18, 19 are communicated with each other,and their chamber interiors are maintained at the air pressure A.Therefore, the piston 20 is returned until a position shown by atwo-dotted chain line in FIG. 1, i.e., a starting position of the strokein a small state of the reaction force F (S6 to S7 to END in FIG. 3)

[0062] As shown by a vertical arrow in an “END” position in FIG. 3, theupper chamber 18 is opened to the atmosphere, etc. by switchingpositions of the electromagnetic valve 113 so that the compressed airleft within the upper chamber 18 can be forcedly discharged and thepiston 20 can be returned to the original position.

[0063] Further, when no piston 20 is returned until the final positionfor some reasons, the air within the upper chamber 18 is also dischargedby switching the electromagnetic valve 113, and the piston 20 can beforcedly returned to the original position.

[0064] In accordance with such an embodiment mode, there are thefollowing effects.

[0065] (1) When molding is started and external force P begins to beapplied to the die cushion device 1, the piston 20 compresses the airwithin the lower chamber 19 while a sealing state of the upper and lowerchambers 18, 19 is maintained. Accordingly, large reaction force Fagainst this external force P can be generated. When the piston 20 isfurther continuously lowered, the reaction force F can be reduced bycommunicating the upper and lower chambers 18, 19 with each other by theswitching portion 33 of the spool 30. Thereafter, the air within thelower chamber 19 is again compressed and large reaction force F can begenerated by interrupting and closing the flow path between the upperand lower chambers 18, 19.

[0066] Thus, in this embodiment mode, die cushion ability (reactionforce F) can be switched during one stroke of the piston 20. Inparticular, the reaction force F is increased at a starting time of themolding, and is reduced at an intermediate time of the molding, and isagain increased at a final time of the molding. Thus, a holding degreeof the thin plate material using a blank holder, etc. can be changed,and it is possible to preferably cope with the deep drawing molding ofthe thin plate material.

[0067] (2) In this case, the reaction force F is mechanically switchedin association with the stroke of the piston 20 by the spool 30 arrangedwithin the cylinder 10 and extending through the piston 20. Therefore,the die cushion device can be set such that no time lag at a switchingtime is easily caused, and the reaction force F can be instantlyswitched.

[0068] (3) Since the reaction force F is switched by the spool 30 withinthe cylinder 10, it is not necessary to arrange a complicated mechanismoutside the cylinder 10 so that structure can be simplified.

[0069] Further, when the reaction force F is changed in separate timing,etc., it is sufficient to set a separate spool instead of the spool 30so that it is possible to easily cope with another molding.

[0070] (4) Since the spool 30 is also used as a guide member of thepiston 20 by extending through the piston 20, the piston 20 can be morereliably and smoothly slid in the vertical direction.

[0071] (5) The piston 20 is formed in a disk shape and the pressurereceiving area of the lower face 27 is larger by the sectional area ofthe rod 21 than the pressure receiving area of the upper face 26.Therefore, when no external force P is applied and the pressures withinthe upper and lower chambers 18, 19 are set to the same, the piston 20can be automatically raised so that no special raising mechanism isrequired and the structure can be further simplified.

[0072] (6) Since the check valve 144 is arranged in the bypass flow path143 between the flow paths 112 and 142, the check valve 144 can beopened when the air pressure within the upper chamber 18 is equal to orgreater than the air pressure within the lower chamber 19. Therefore,when the piston 20 begins to be returned to the original position, theair pressure within the upper chamber 18 can be discharged and escapedto a side of the flow path 142 even when the air within the upperchamber 18 is compressed. Accordingly, the interiors of the upper andlower chambers 18, 19 can be maintained at the air pressure A withoutsubstantially compressing the air within the upper chamber 18, and thepiston 20 can be reliably raised to the uppermost position.

[0073] (7) The electromagnetic valve 113 for forcedly exhausting the airleft within the upper chamber 18 is arranged in the cylinder 10.Accordingly, even when the left air becomes resistance and no piston 20is returned until the uppermost position, the left air can be exhaustedby switching the electromagnetic valve 113 so that disadvantages can berapidly avoided.

[0074] A second embodiment mode will next be explained.

[0075]FIG. 4 shows a sectional view of a die cushion device 2 inaccordance with the second embodiment mode of the invention.

[0076] In FIG. 4, the same functional members as the first embodimentmode are designated by the same reference numerals, and their detailedexplanations are omitted or simplified here. The detailed explanationsare similarly omitted or simplified with respect to other embodimentmodes and modified examples explained later.

[0077] In the die cushion device 2, a separate cylinder 210 is arrangedin series and integrally below the cylinder 10. A piston 220 slid withinthe cylinder 210 is connected to a lower portion of the piston 20through a rod 221. An upper chamber 218 is formed above the piston 220within the cylinder 210, and a lower chamber 219 is formed below thepiston 220.

[0078] An insertion hole 212 inserting the rod 221 of the piston 220thereinto is arranged in a partition wall portion 101 between thecylinders 10 and 210, and an unillustrated sealant is arranged aroundthe insertion hole 212 and the piston 220. Thus, the airtight propertybetween the lower chamber 19 of the cylinder 10 and the upper chamber218 of the cylinder 210 is secured. Further, volumes of the cylinders10, 210 are optionally determined in their operations, but are set to beapproximately the same in this embodiment mode.

[0079] Similar to the cylinder 10, an exhaust port 311, a flow path 312,an electromagnetic valve 313, an air intake port 341, a flow path 342, abypass flow path 343 and a check valve 344 are arranged in the cylinder210.

[0080] An insertion hole 102 of a spool 30 is arranged in the partitionwall portion 101 between the cylinders 10 and 210, and a sealant 103 isarranged in the insertion hole 102. An insertion hole 215 of the spool30 is arranged in a bottom face portion 214 of the cylinder 210, and asealant 217 is arranged in this insertion hole 215.

[0081] A communication hole 223 is vertically communicated in the piston220, and the spool 30 extends through the interior of the communicationhole 223. A sealant 224 is arranged in this communication hole 223.

[0082] On the other hand, the spool 30 is arranged such that the spool30 extends through both the pistons 20, 220. The spool 30 has aswitching portion 33 located within the cylinder 10, and a separateswitching portion 233 located within the cylinder 210. The switchingportion 233 has a length shorter than that of the switching portion 33.

[0083] An upper large diameter portion 34 is located on an upper side ofthe switching portion 33, and a lower large diameter portion 35 islocated on a lower side of the switching portion 33. An upper largediameter portion 234 continuously connected to the lower large diameterportion 35 is located on an upper side of the switching portion 233, anda lower large diameter portion 235 is located on a lower side of theswitching portion 233.

[0084] In the above embodiment mode, one control means is constructed bythe piston 20 having the communication hole 23, and an upper sideportion of the spool 30 having the switching portion 33. Another controlmeans is constructed by the piston 220 having the communication hole223, and a lower side portion of the spool 30 having the switchingportion 233. Accordingly, plural (two in this embodiment mode) controlmeans are arranged.

[0085] In such a die cushion device 2 of the present embodiment mode,when the pistons 20, 220 located in uppermost positions within thecylinders 10, 210 are lowered by unillustrated external force P, boththe airs within the lower chambers 19, 219 are simultaneously compressedso that unillustrated reaction force F is generated.

[0086] When the pistons 20, 220 are further lowered, the communicationhole 23 of the piston 20 first reaches the switching portion 33, and theupper and lower chambers 18, 19 begin to be communicated with each otherso that the reaction force F is damped. However, at this stage, nocommunication hole 223 of the piston 220 reaches a position forcommunicating the lower chambers 218, 219 with each other (a state ofFIG. 4) since the length of the switching portion 233 is short. Thelower chamber 219 is continuously compressed by the piston 220 as it is.

[0087] Since the pistons 20, 220 are further lowered, the upper andlower chambers 218, 219 are also communicated with each other by thecommunication hole 223 while the communication state between the upperand lower chambers 18, 19 is continued by the communication hole 23. Thereaction force F is reduced until a minimum level.

[0088] Thereafter, when the pistons 20, 220 are further lowered, therespective sealants 24, 224 of the communication holes 23, 223simultaneously interrupt the flow path between the upper and lowerchambers 18, 19 and the flow path between the upper and lower chambers218, 219. Thus, the air within each of the lower chambers 19, 219 iscompressed so that the reaction force F is again raised.

[0089] When the slide is raised, the pistons 20, 220 are automaticallyraised by the difference in area between upper and lower faces 226, 227.The principle in this case is the same as the first embodiment mode.

[0090] In accordance with this embodiment mode, the above effects (1) to(7) can be similarly obtained by a construction similar to that of thefirst embodiment mode, and the following effects can be also obtained bythe peculiar construction having two control means.

[0091] (8) That is, in the die cushion device 2, timing forcommunicating the upper and lower chambers 18, 19 with each other andtiming for communicating the upper and lower chambers 218, 219 with eachother are shifted from each other during one stroke of each of thepistons 20, 220 by arranging the two switching portions 33, 233 in thespool 30 and setting lengths of these switching portions to be differentfrom each other. Accordingly, magnitude of the reaction force F can bestepwise damped at two stages so that the die cushion device 2 can beset to a multistage type.

[0092] (9) Further, since both the lower chambers 19, 219 formed withinthe two cylinders 10, 210 are compressed by the pistons 20, 220, it ispossible to approximately generate double reaction force F in comparisonwith the die cushion device 1 of the first embodiment mode in which onlyone lower chamber 19 is compressed. Therefore, die cushion ability canbe increased.

[0093] A third embodiment mode will next be explained.

[0094]FIG. 5 shows a die cushion device 3 in accordance with the thirdembodiment mode of the invention. The illustration of a sealant isomitted in FIG. 5.

[0095] The die cushion device 3 greatly differs from the first andsecond embodiment modes in that a switching device 40 is arrangedoutside the cylinder 10, and inflow and outflow of the air between theupper and lower chambers 18, 19 are mechanically controlled by a controlmeans constructed by this switching device 40. Accordingly, no spool 30as in the first and second embodiment modes is arranged in the cylinder10 of the die cushion device 3, and no communication hole 23, etc. arealso arranged in the piston 20.

[0096] Reference numeral 50 in FIG. 5 designates a pressure supplysource constructed by a tank 51 functioning as e.g., an accumulator, anda pressure reducing valve 52. The pressure supply source 50 suppliescompressed air having a predetermined pressure to the lower chamber 19of the cylinder 10 through a flow path 142.

[0097] The switching device 40 has a rack 41 arranged in a die cushionpad 22 and vertically moved together with the piston 20, a rotatedpinion gear 42 engaged with the rack 41, and a rotary valve 43 operatedby rotating the pinion gear 42.

[0098] In the rotary valve 43, a first port 432 formed in a sleeve 431and a flow path 142 are communicated with each other by a flow path 433,and a second port 434 and the upper chamber 18 are communicated witheach other by a flow path 435, and a third port 436 is opened to theatmosphere.

[0099] As enlargedly shown in FIG. 6, a pair of concave switchingportions 438, 439 is arranged in a rotor 437 of the rotary valve 43 suchthat the switching portions 438, 439 are spaced from each other in acircumferential direction. The switching portion 438 has a function forcommunicating the first and second ports 432, 434 with each other. Theswitching portion 439 has a function for communicating the second andthird ports 434, 436 with each other.

[0100] An operation of the die cushion device 3 performed by a stroke ofthe piston 20 will next be explained on the basis of FIGS. 5, 7(A),7(B), and 7(C).

[0101]FIG. 7(A): When the piston 20 is located in an uppermost position,the switching portion 438 is located on a side of the first port 432 inthe rotor 437 of the rotary valve 43, and the flow path between theupper and lower chambers 18, 19 within the cylinder 10 is interrupted bythe rotor 437. Accordingly, when the piston 20 is lowered byunillustrated external force P from this state, the air within the lowerchamber 19 is compressed and unillustrated large reaction force F isobtained.

[0102]FIG. 7(B): When the rotor 437 is rotated in the counterclockwisedirection as the piston 20 is lowered, the first and second ports 432,434 are gradually communicated with each other by the switching portion438. Thus, the upper and lower chambers 18, 19 are communicated witheach other and the air is moved so that the interiors of these chambersinstantly become an equal pressure. In this state, the reaction force Fagainst the external force P is instantly reduced.

[0103]FIG. 7(C): When the piston 20 is further lowered and the firstport 432 is closed by the rotor 437, the flow path between the upper andlower chambers 18, 19 is interrupted and the air within the lowerchamber 19 is compressed so that the reaction force F is again raised.Thereafter, when a slide is raised, the piston 20 is automaticallyraised and the rotor 437 is rotated in the clockwise direction.

[0104] When the piston 20 is returned until a position near theuppermost position, the second and third ports 434, 436 are communicatedwith each other by the switching portion 439 as shown in FIG. 7(A) sothat the air is exhausted from the interior of the upper chamber 18.Thus, the pressure within the upper chamber 18 is exhausted, and thepiston 20 is reliably returned to the uppermost position before thepiston 20 begins to be lowered. That is, the third port 436 and theswitching portion 439 function as a pressure exhaust means in theinvention.

[0105] In accordance with this embodiment mode, inflow and outflow ofthe air between the upper and lower chambers 18, 19 can be mechanicallycontrolled in association with the stroke of the piston 20 by arrangingthe switching device 40. Therefore, the above effects (1) and (2) can besimilarly obtained and the object of the invention can be achievedalthough the construction is different. Further, the above effect (5)can be also obtained by a construction similar to that of each of thefirst and second embodiment modes. Further, the above effect (6) can besimilarly obtained since one portion of the rotary valve 43 functions asthe pressure exhaust means.

[0106] In addition, there are the following effects by the peculiarconstruction of this embodiment mode.

[0107] (10) Since the switching device 40 for controlling the inflow andoutflow of the air between the upper and lower chambers 18, 19 isarranged outside the cylinder 10, the die cushion device 3 can be setsuch that no switching device 40 is easily restricted in structure,etc., in comparison with a case in which the switching device 40 isarranged within the cylinder 10. Accordingly, cost can be reduced byfreely designing the die cushion device to a certain degree.

[0108] A fourth embodiment mode will next be explained.

[0109]FIG. 8 shows a die cushion device 4 in the fourth embodiment modeof the invention. The illustration of a sealant is also omitted in FIG.8.

[0110] In the die cushion device 4, the construction of a switchingdevice 60 as a control means arranged outside the cylinder 10 greatlydiffers from that of the switching device 40 of the third embodimentmode. The other constructions are approximately the same as the thirdembodiment mode.

[0111] The switching device 60 has a guide member 61 arranged in a diecushion pad 22 and vertically moved together with this die cushion pad,a spool valve 62 switched in accordance with a vertical position of theguide member 61, and an air reservoir device 63 communicated with thespool valve 62.

[0112] A taper face 611 is formed in the guide member 61, and this taperface 611 is linearly inclined so as to be separated from the cylinder 10as this taper face 611 is directed downward.

[0113] A shape of the taper face 611, etc. may be optionally determinedin accordance with how to generate an operating speed of the spool valve62 and unillustrated reaction force F. For example, the operating speedof the spool valve 62 may be increased by increasing an inclinationangle. Further, the operation of the spool valve 62 may be substantiallystopped and the spool valve 62 may be reversely operated during onestroke by arranging a vertical face in an intermediate portion of thetaper face 611, or arranging a taper face reversely inclined in theintermediate portion.

[0114] In the spool valve 62, a first port 622 formed in a sleeve 621and a flow path 142 are communicated with each other by a flow path 623,and a second port 624 and the upper chamber 18 are communicated witheach other by a flow path 625, and a third port 626 and the airreservoir device 63 are communicated with each other by a flow path 627.

[0115] A spool 628 is stored into the sleeve 621 and is slid within thissleeve 621, and has a switching portion 628A and left-hand andright-hand large diameter portions 628B, 628C. A roller 629A of a rod629 arranged at one end of this spool 628 is rolled on the taper face611 of the guide member 61. In this case, the roller 629A is biased soas not to be separated from the taper face 611 at any time by a spring629B, etc. on the other side of the spool 628.

[0116] The air reservoir device 63 stores the air from the upper chamber18 without exhausting this air into the atmosphere when the pressurewithin the upper chamber 18 is exhausted. The air reservoir device 63has a cylinder 631 and a piston 633 biased by a spring 632. One ofspaces within the cylinder 631 partitioned by the piston 633 is an airreservoir space of a variable volume type, and the other space storingthe spring 632 thereinto is opened to the atmosphere.

[0117] The construction of the air reservoir device is not limited tothis construction, but, for example, a construction similar to that of arubber balloon expanded and contracted in accordance with an internalair amount may be also optionally applied An operation of the diecushion device 4 performed by the stroke of the piston 20 will next beexplained on the basis of FIGS. 8, 9(A), 9(B), and 9(C).

[0118]FIG. 9(A): When the piston 20 is located in an uppermost position,the spool 628 of the spool valve 62 is located on sides of the secondand third ports 624, 626, and the flow path between the upper and lowerchambers 18, 19 within the cylinder 10 is interrupted by the spool 628.Accordingly, when the piston 20 is lowered by unillustrated externalforce P from this state, the air within the lower chamber 19 iscompressed and unillustrated large reaction force F is obtained.

[0119]FIG. 9(B): When the roller 629A is rolled on an upper portion sideof the taper face 611 as the piston 20 is lowered, the spool 628 isgradually moved onto the left-hand side of this figure. The first andsecond ports 622, 624 are communicated with each other by the switchingportion 628A so that the upper and lower chambers 18, 19 arecommunicated with each other and the air is moved and the interiors ofthese chambers instantly become an equal pressure. In this state,similar to the third embodiment mode, the reaction force F against theexternal force P is instantly reduced.

[0120]FIG. 9(C): When the piston 20 is further lowered and the secondport 624 is closed by the right-hand large diameter portion 628C of thespool 628, the flow path between the upper and lower chambers 18, 19 isinterrupted and the interior of the lower chamber 19 is compressed, andthe reaction force F is again raised. Thereafter, when the slide israised, the piston 20 is automatically raised and the spool 628 is movedonto the right-hand side.

[0121] When the piston 20 is returned until a position near theuppermost position, the second and third ports 624, 626 are communicatedwith each other by the switching portion 628A, and the air within theupper chamber 18 is moved into the air reservoir device 63 as shown inFIG. 8. Thus, the pressure within the upper chamber 18 is exhausted, andthe piston 20 is reliably returned to the uppermost position before thepiston 20 begins to be lowered. That is, in this embodiment mode, thethird port 626 and the switching portion 628A function as the pressureexhaust means in the invention.

[0122] In this embodiment mode, effects similar to those in the thirdembodiment mode can be obtained although the construction of theswitching device 60 is different. Further, there are the followingeffects by the peculiar construction of the switching device 60.

[0123] (11) Since the switching device 60 in this embodiment mode hasthe air reservoir device 63, no air compressed within the upper chamber18 is exhausted to the atmosphere, etc. so that the operating air can beeffectively utilized and unnecessary energy consumption can berestrained.

[0124] (12) It is sufficient to change the shape of the taper face 611of the guide member 61 to set generating degrees of the reaction force Fto be different from each other. However, since the guide member 61 isarranged outside the cylinder 10, an exchanging work of another guidemember can be easily and rapidly made, and a planning time can begreatly shortened.

[0125] The invention is not limited to each of the above embodimentmodes, but other constructions able to achieve the object of theinvention, etc. are included, and modifications, etc. shown below arealso included in the invention.

[0126] For example, in the first and second embodiment modes, the checkvalves 144, 344 arranged outside the cylinder 10 are used as thepressure exhaust means in the invention. However, in addition, as shownin FIG. 10, a check valve 70 arranged in the piston 20 may be also used.

[0127] This check valve 70 is attached into a through flow path 18extending through the piston 20. When the interiors of the upper andlower chambers 18, 19 are set to an equal pressure, or when the pressurewithin the upper chamber 18 begins to exceed the pressure within thelower chamber 19, an opening-closing member 72 opens the through flowpath 28 by the biasing force of a spring 71 so that the equal pressurestate within the upper and lower chambers 18, 19 is maintained. Thus,when the piston 20 is automatically raised, the air compressed withinthe upper chamber 18 is returned to the lower chamber 19 through thethrough flow path 28, and the piston 20 can be reliably returned untilthe uppermost position.

[0128] On the other hand, while the interior of the lower chamber 19 iscompressed, the air pressure within the lower chamber 19 exceeds thebiasing force of the spring 71, and pushes up the opening-closing member72 so that the through flow path 28 is blocked Thus, at a moldingstarting time and a molding final stage using a press, the through flowpath 28 is blocked by the opening-closing member 72 and the air withinthe lower chamber 19 can be reliably compressed so that large reactionforce F can be obtained.

[0129] Further, in such a construction, since no air is exhausted to theexterior of the cylinder 10, energy loss can be reduced.

[0130] Such a construction may be also applied to the piston 20 of thedie cushion device externally having the switching device as in thethird and fourth embodiment modes. In this case, it is possible toremove the third ports 436, 626 of the sleeves 431, 621, etc.

[0131] In the first and second embodiment modes, the sealants 24, 224are arranged within the communication holes 23, 223 of the pistons 20,220. However, for example, as shown in FIG. 11, an annular sealant 25maybe also arranged in each of the large diameter portions 34, 334 andthe lower large diameter portions 35, 335 of the spool 30.

[0132] Further, the die cushion devices 1 to 4 of the respectiveembodiment modes are constructed such that the reaction force F isincreased at the starting time of molding using a press, and is reducedat the intermediate time of the molding, and is again increased at thefinal time of the molding. However, the reaction force F may beoptionally changed during one stroke, and may be appropriatelydetermined in the operation of the die cushion device. Accordingly, forexample, the reaction force F may be reduced at 30 the starting andfinal times of the molding, and large reaction force F may be generatedat the intermediate time of the molding. Further, large reaction force Fmay be generated at the molding starting time, and, thereafter, smallreaction force F may be generated until the molding final time.Conversely, small reaction force F may be generated at the moldingstarting time, and, thereafter, large reaction force F may be generateduntil the molding final time. Such cases are also included in theinvention.

[0133] In the second embodiment mode, the die cushion device is set to amultistage type by arranging the switching portions 33, 233 above andbelow one spool 30, but is not limited to this type. For example, a diecushion device at plural stages may be also realized by arranging pluralspools extending through the piston within one cylinder, and arrangingswitching portions in the respective spools, and shifting positions ofthe respective switching portions from each other.

[0134] Shapes of the rotor 437 and the spool 628 used in the third andfourth embodiment modes may be devised and rotors 437 and spools 628 maybe also added in number to realize the die cushion device of themultistage type.

What is claimed is:
 1. A die cushion device comprising: a cylinder; apiston; first and second chambers arranged within said cylinder andseparated by said piston sliding within said cylinder; and control meansfor controlling inflow and outflow of a fluid between said first andsecond chambers in association with a stroke of said piston.
 2. A diecushion device according to claim 1, wherein said control means includesa valve arranged within said cylinder.
 3. A die cushion device accordingto claim 1, wherein said control means includes a switching devicearranged outside said cylinder.
 4. A die cushion device according toclaim 1, wherein said piston is slid by a rod, and further comprisingpressure exhaust means for exhausting a fluid pressure within said firstchamber on said rod side.
 5. A die cushion device according to claim 2,wherein said piston is slid by a rod, and further comprising pressureexhaust means for exhausting a fluid pressure within said first chamberon said rod side.
 6. A die cushion device according to claim 3, whereinsaid piston is slid by a rod, and further comprising pressure exhaustmeans for exhausting a fluid pressure within said first chamber on saidrod side.
 7. A die cushion device according to claim 1, wherein aplurality of said control means are arranged.
 8. A die cushion deviceaccording to claim 2, wherein a plurality of said control means arearranged.
 9. A die cushion device according to claim 5, wherein aplurality of said control means are arranged.
 10. A die cushion deviceaccording to claim 3, wherein a plurality of said control means arearranged.
 11. A die cushion device according to claim 4, wherein aplurality of said control means are arranged.
 12. A die cushion deviceaccording to claim 6, wherein a plurality of said control means arearranged.